A Mechanism for the Dependence of Moisture Detection Sensitivity on Gas Composition in Residual Gas Analysis

The measurement of internal water vapor in semiconductor packages by Residual Gas Analysis (RGA) is complicated by the dependence of the detected signal on gas composition. In particular, the dependence on the percentage of O2 or H2 present is quite significant. The data presented show that the detected moisture signal contains an additive portion proportional to the percentage O2 or H2 present, but is independent of the true water present. A mechanism, sputtering or local heating in the ionizer of the mass spectrometer, is shown to account for this behavior.